How to Make Underground Speaking Tubes

Here's a fun trick for when you want to send messages without using any power.

By
Matt Woods

Aug 2, 2017

Speaking tubes, once standard issue on naval vessels as a guaranteed way to send messages without relying on power, were important enough that in 1926 the Navy's Bureau of Construction and Repair commissioned "Transmission of Sound Through Voice Tubes," a meticulous study that drew on science experiments, calculus, and a ridiculous canvas helmet with tubes for earpieces. According to Matt Woods of the Intrepid Sea, Air & Space Museum, voice pipes could carry sound up to about 300 feet. He helped us design one for the backyard with modern touches, including a slot for a smartphone (for tunes), and a swivel to aim the sound. Ships used metal to avoid corrosion, but 4-inch PVC is cheaper and easier to work with. Find a part of your yard to bury the tube, then pick locations for the ends and start digging.

Materials

• 4" PVC pipe, length based on path of tube

• four 4" elbow joints

• four 4" couplings

• additional joints for path

• two 4" x 6" reducing couplings

• PVC primer and glue

• scrap wood

• dry graphite lubricant

• Krazy glue

• chicken wire

Tools

• miter saw

• shovel

• jigsaw

Step 1: Dig a route for the underground run that is large enough to accommodate your PVC. Straighter routes are better, as joints can degrade the integrity of the tube and allow some sound to escape.

Step 2: At each end of the run, use an elbow to direct the pipe vertically out of the ground. Cut to an appropriate height and glue a coupling on top. If necessary—maybe you decided to run the tube into a tree fort—support it by bracketing it to a solid surface.

Step 3: Cut a 3-inch piece of pipe with a miter saw. Glue an elbow to one end, and lubricate the other end with graphite. Press the lubricated end into the coupling and ensure it swivels easily.

Step 4: To add the phone slot, cut a 10-inch piece of PVC with a miter saw. Trace the bottom of your phone on the middle of the pipe and cut ¼ inches around that line with a jigsaw. Inside the PVC, glue a small piece of scrap wood under the hole to keep the phone propped up, so the sound won't be muffled. Glue the PVC piece to the elbow on top of the swivel.

Step 5: To close off the system when a phone is not being used, lubricate a coupling and put it on the 10-inch piece of PVC (cut it in half with a miter saw if it has a ridge inside that keeps it from sliding into place). Ensure it rotates freely on the pipe. Remove the coupling from the pipe and trace your phone on it, cutting a hole to match the one on the PVC pipe. When the holes are aligned, the phone can be dropped in. When the phone is not in use, rotate the coupling to close the hole.

Step 6: Form a horn on the end of the tube by gluing on a reducing coupling. Cut a circular piece of chicken wire and use Krazy glue to affix it a few inches back in the opening to block rodents and wayward toys.

Step 7: Repeat this process on the other end of the tube.

Matt Woods is senior vice president of facilities, engineering and security, Intrepid Sea, Air & Space Museum. This originally appeared in the September 2017 issue.

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